On Wednesday, 04/05/2006 at 11:42 CST, Tyler Koyl <[EMAIL PROTECTED]>
wrote:
>> I am quite sure this exists but I need a little help.
>> I was wondering if there is a way to place a z/VM 5.1 linux guest into a
froozen
>> state? ...
And on Wednesday 05 April 2006 15:48, Alan Altmark responded:
>Image backups like that won't do what you want. Linux has data in its
>internal buffer cache that needs to be written to dasd and that only
>happens when you unmount the filesystem from Linux or shut Linux down.
Linux I/O buffers are also written to DASD by the sync(1) command, so you
don't have to unmount or shut down to get the data written. But of course,
that doesn't do you any good. Sync is not atomic, so there is no point of
time in which all filesystems are consistent. Also, other processes may well
be creating new dirty I/O buffers while the sync is in progress.
From a Linux standpoint, the only way you could manage this is to suspend all
running processes (other than the kernel ones and your own), do a sync, snap
the DASD, then continue those processes. But even that only ensures that the
filesystems are consistent, not that the contents of the files are consistent
from an application's point of view. That is, if you recovered that snapped
DASD and booted Linux, your apps might not like the data they read in.
I'm trying to think of an approach that would be faster than the entire
shutdown/reboot sequence. Bringing it down to single-user mode, syncing,
snapping and then back to the default mode would be a little bit faster, and
it would stop all apps so their data would be saved in a consistent state,
but that's not really a whole lot faster than a complete reboot. You're
pretty much going to have to have some downtime.
- MacK.
-----
Edmund R. MacKenty
Software Architect
Rocket Software, Inc.
Newton, MA USA
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